In certain operations, such as cholecystectomy and obesity surgery, a spreading of the legs of a patient arranged on the patient bearing surface of an operating table is required. For this, the thighs and shins of the patient are arranged on a thigh plate and a shin plate, which can pivot relative to each other and to other segments of the patient bearing surface.
For the spreading of the legs, the thigh plate and the shin plate attached to it are each pivoted about a pivot axis oriented perpendicular to the patient bearing surface. In addition to this, it may be necessary to pivot the shin plates about another pivot axis oriented perpendicular to their longitudinal axis, in order to achieve a suitable positioning of the patient, e.g., a knee/elbow posture. Owing to the different anatomy of patients, the pivot axes of the patient bearing surface generally do not run through the joints of the patient. This may result in a physiologically disadvantageous posture of the patient after a pivoting of the shin and/or thigh plates, in which the ligaments of the patient are strained, requiring a subsequent position correction of the patient.
A knee/elbow posture of the patient is required, for example, in spinal operations and rectal procedures. In this case, the patient is supported primarily on his knees and his upper torso. For this, the knees of the patient are placed on the shin plates, which are lowered with respect to the region of the patient bearing surface supporting the elbows and the upper torso. A secure and favorable supporting of the patient for the operation requires varying the spacing of the shin plates, without changing their parallel orientation to the region of the patient bearing surface supporting the upper torso.
From DE 102 53 906 A1 there is known a patient bearing surface having a variable-position pivot axis for the pivoting of a shin plate relative to a thigh plate. A four-bar linkage is provided here, from which the variable-position pivot axis is arranged at a spacing. As a result of the spacing of the pivot axis from the four-bar linkage, the detaining or releasing of the detention of the four-bar linkage and the pivot axis requires two activation steps, one for a control element for the four-bar linkage and one for the pivot axis. Furthermore, the arrangement of the leg plates does not allow for any knee/elbow posture in which the shin plates can be varied in their position while maintaining their orientation.
Moreover, in the known four-piece leg plates which are suitable for the knee/elbow posture it is not possible to pivot the leg plates outward by an angle greater than 100° relative to the longitudinal axis of the patient bearing surface. Therefore, the leg plates have to be removed during medical procedures during which the leg plates are temporarily unnecessary, which requires further work on the part of the technicians.
Thus, the leg plates can pivot about various joints and should be adjustable as much as possible optimally to the patient being supported. For this reason, the joints are at best continuously adjustable in design. Yet these have the drawback, on the one hand, of having to produce and switch large forces in order to generate the required frictional force, which may result in large activating forces. On the other hand, friction couplings are often subject to wear, so that the properties over the course of time become altered. For this reason, form-fitting couplings are readily used for such joint blocks. Often one uses here Hirth couplings or crown gear couplings. Yet these have the drawback that the individual teeth of the coupling element have to become large if one wishes to transmit large forces, whereas a sensitive small-angle adjustment requires a corresponding division resulting in very small teeth. A frequent compromise is achieved in that the diameter of the crown gear is increased so that one can design a sufficiently large number of teeth with adequate dimensions. But this takes up space and results in increased weight for the overall apparatus.
In all these supporting systems, no danger to the patient may occur at any time. This might happen, for example, if a leg drops down without control, or if the entire patient slips off the bearing surface, because the user accidentally opens a fixed position of the joint mechanism. Another danger might arise when leg plates which are arranged on motorized joint modules are moved individually and positioned one above the other. Since only a small portion of the patient is not covered by cloths during the operation, the control of these wrong positions is not always easy for the operator and it must be prevented as much as possible by the engineering.
Because of the many joints and the interface between leg plate and bearing surface, as well as thigh plate and shin plate, there are a multitude of control element. Now, it may happen that a user who would like to perform an adjustment of the leg plate reaches into the dimly lit region beneath the covering cloths of the OR table and activates a control element. But it should not happen that he or she accidentally activates the wrong control element, as this might have detrimental consequences and fatal consequences.